media-fonts/sarasa-gothic: add 1.0.21, drop 1.0.20

[Linerre]

close #5281

[github-actions[bot]]

:heavy_check_mark: pkgcheck checks passed

• pkgcheck 0.10.30
• the corresponding ::gentoo commit: https://github.com/gentoo-mirror/gentoo/commit/1fae52f34bb2da9e06a26a3968b420263b569b05